Polarization-Multiplexed Multilevel Differential Phase Shift Keyed Signal Detector

Abstract

An apparatus and method for detecting a PMUX multilevel DPSK signal having at least two polarization components with equal symbol periods, which comprises utilizing two polarization-independent Optical Delay Interferometers (ODIs), detecting the four outputs of the two ODIs with two balanced detectors, and digitizing the two detected electronic signals at a sampling rate of twice the symbol rate of the said polarization component signals.

1 . An apparatus for recovering the in-phase and quadrature-phase components for each polarization of a polarization-multiplexed DmPSK signal, comprising:
 a detection stage for contemporaneously detecting in-phase and quadrature-phase components for both polarizations of a polarization-multiplexed DmPSK signal to produce an in-phase components signal and a quadrature-phase components signal;   a digitizing stage for digitizing each of the in-phase and quadrature-phase components signals at a sample rate of at least twice the symbol rate; and   a deinterleaving stage for deinterleaving the digitized in-phase and quadrature-phase components signals to provide, respectively, the in-phase components for each polarization and the quadrature-phase components for each polarization.   
   
   
       2 . The apparatus of  claim 1 , wherein the detection stage comprises:
 a power divider responsive to said signal, for providing thereby first and second divided signals;   a pair of polarization-independent optical delay interferometers responsive to said first and second divided signals for outputting a pair of in-phase signals for both polarizations, and contemporaneously a pair of quadrature-phase signals for the first and second polarization components;   a first balanced detector for receiving the pair of in-phase signals for both polarizations, and providing thereby a first electronic signal; and   a second balanced detector for receiving the pair of quadrature-phase signals for both polarizations, and providing thereby a second electronic signal.   
   
   
       3 . The apparatus of  claim 1 , wherein the digitizing stage comprises:
 a first digitizer operating at twice the symbol rate of the multilevel DPSK signal for receiving the first electronic signal, and providing thereby a first digital output; and   a second digitizer operating at twice the symbol rate of the multilevel DPSK signal for receiving the second electronic signal, and providing thereby a second digital output.   
   
   
       4 . The apparatus of  claim 1 , wherein the deinterleaving stage comprises:
 a first deinterleaver for receiving the first digital output, and providing thereby separate digital representations for the in-phase data symbols for both polarizations; and   a second deinterleaver for receiving the second digital output, and providing thereby separate digital representations for the quadrature-phase data symbols for both polarizations.   
   
   
       5 . The apparatus of  claim 2 , wherein the first and second polarization components of the signal are orthogonally polarized with respect to each other. 
   
   
       6 . The apparatus of  claim 2 , wherein the first and second polarization components are offset in time by substantially half the symbol period of the multilevel DPSK signal. 
   
   
       7 . The apparatus of  claim 2 , wherein the first and second polarization components are of return-to-zero format. 
   
   
       8 . The apparatus of  claim 2 , wherein the pair of optical delay interferometers have a delay of substantially the symbol period of the multilevel DPSK signal. 
   
   
       9 . The apparatus of  claim 2 , wherein the two optical delay interferometers differ in phase offset by substantially  90  degrees. 
   
   
       10 . The apparatus of  claim 1 , wherein the first digitizer and the second digitizer are binary decision circuits each providing a digital binary output. 
   
   
       11 . An apparatus for detecting a polarization-multiplexed multilevel DPSK signal having first and second polarization components, comprising:
 a power divider responsive to said signal, for providing thereby first and second divided signals;   a pair of polarization-independent optical delay interferometers responsive to said first and second divided signals for outputting a pair of in-phase signals for the first and second polarization components, and contemporaneously a pair of quadrature-phase signals for the first and second polarization components;   a first balanced detector for receiving the pair of in-phase signals for the first and second polarization components, and providing thereby a first electronic signal.   a second balanced detector for receiving the pair of quadrature-phase signals for the first and second polarization components, and providing thereby a second electronic signal;   a first digitizer operating at twice the symbol rate of the multilevel DPSK signal for receiving the first electronic signal, and providing thereby a first digital output;   a second digitizer operating at twice the symbol rate of the multilevel DPSK signal for receiving the second electronic signal, and providing thereby a second digital output;   a first deinterleaver for receiving the first digital output, and providing thereby separate digital representations for the in-phase data symbols for the first and second polarization components; and   a second deinterleaver for receiving the second digital output, and providing thereby separate digital representations for the quadrature-phase data symbols for the first and second polarization components.   
   
   
       12 . The apparatus of  claim 11 , wherein the first and second polarization components of the polarization-multiplexed multilevel DPSK signal are orthogonally polarized with respect to each other. 
   
   
       13 . The apparatus of  claim 11 , wherein the first and second polarization components are offset in time by substantially half the symbol period of the multilevel DPSK signal. 
   
   
       14 . The apparatus of  claim 11 , wherein the first and second polarization components are of return-to-zero format. 
   
   
       15 . The apparatus of  claim 11 , wherein the pair of optical delay interferometers have a delay of substantially the symbol period of the multilevel DPSK signal. 
   
   
       16 . The apparatus of  claim 11 , wherein the two optical delay interferometers differ in phase offset by substantially 90 degrees. 
   
   
       17 . The apparatus of  claim 11 , wherein the signal is a polarization-multiplexed D8PSK signal. 
   
   
       18 . The apparatus of  claim 11 , wherein the first digitizer and the second digitizer are binary decision circuits each providing a digital binary output. 
   
   
       19 . The apparatus of  claim 11 , wherein the first digitizer and the second digitizer are analog-to-digital converters each providing a digital multilevel output. 
   
   
       20 . The apparatus of  claim 19 , wherein the resolution of said analog-to-digital converters is substantially 5 bits. 
   
   
       21 . The apparatus of  claim 19 , wherein the first and second deinterleavers are configured to obtain four digital multilevel representations for the in-phase and quadrature-phase data symbols of the first and second polarization components. 
   
   
       22 . The apparatus of  claim 21 , wherein said four digital multilevel representations are received and processed by a digital signal processor to enhance the receiver sensitivity. 
   
   
       23 . The apparatus of  claim 21 , wherein said four digital multilevel representations are received and processed by a digital signal processor to mitigate transmission impairments. 
   
   
       24 . The apparatus of  claim 21 , wherein said four digital multilevel representations are received and processed by a digital signal processor to obtain all original data tributaries of the signal in binary format. 
   
   
       25 . A method, comprising:
 contemporaneously detecting in-phase and quadrature-phase components for both polarizations of a polarization-multiplexed DmPSK signal to produce an in-phase components signal and a quadrature-phase components signal;   digitizing each of the in-phase and quadrature-phase components signals at a sample rate of at least twice the symbol rate; and   deinterleaving the digitized in-phase and quadrature-phase components signals to provide, respectively, the in-phase components for each polarization and the quadrature-phase components for each polarization.